The role of the early viral gene products of SV40 in the establishment of the transformed state of rodent cells. Past experiments have shown that the viral Large-T protein is nearly universally required for the maintenance of such properties as clonal growth or growth in low serum supplement. In rat cells the small-t protein is often required for growth in suspension, activation of serum plasminogen to plasmin, and loss of cytoplasmic actin cable networks. This is not the case with hamster cells where we have been unable to discover any role for small-t in the maintenance of the transformed state. However direct viral tumorigenicity studies indicate that the small-t protein may function as a tumor promotor in hamster cells. Our work in the next year will be directed towards understanding the role of the small-t protein in transformation and tumor induction with emphasis on the mechanism of tumor promotion.